1. Field of the Invention
The present invention relates to an additive used to control puddling in inkjet inks. More specifically, the invention relates to a puddling additive having a nonionic, polar group and a C6-C30 hydrocarbon tail.
2. State of the Art
Inkjet printing is a popular alternative for home and office printing due to the low cost of inkjet printers, advances in quality of the printed images, and the relatively noise-free operation. Notwithstanding these advantages, research and development continue in order to improve inkjet print quality while maintaining a reasonable cost for the inkjet printer and the printing process.
A conventional color inkjet printer comprises a plurality of resistor elements arranged in a particular pattern in a printhead. The resistor elements are located in a chamber that is provided with an opening for inkjet ink to enter from a reservoir. Together, the printhead and the reservoir comprise an inkjet pen. The printhead also includes an orifice plate having a plurality of orifices through which inkjet ink is expelled toward a print medium. Each resistor element is connected by a conductive trace to a microprocessor, where current-carrying signals cause one or more selected resistor elements to heat up. The heat creates a bubble of vapor ink in the chamber, which is expelled through the orifices toward the print medium. The properly sequenced ejection of inkjet ink from each orifice causes characters or other images to be printed on the print medium as the printhead is moved across the print medium. The inkjet printers produce high quality printing and are both compact and affordable. In addition, since only the ink strikes the paper, the inkjet printer is fast and quiet.
To print color images, inkjet printing uses a combination of cyan, magenta, yellow, and, optionally, black inkjet inks to produce all the colors of a color spectrum. The cyan, magenta, yellow, and, optionally, black inkjet inks are referred to collectively as a “set” of inkjet inks. A color inkjet printer typically has four inkjet pens, one pen for each of the inkjet inks. Color inkjet inks are typically aqueous-based and are formulated by dissolving or dispersing a colorant, such as a dye or pigment, in an aqueous ink vehicle. For example, a yellow inkjet ink uses a yellow dye or pigment dissolved or dispersed in the ink vehicle, while a blue inkjet ink uses a cyan dye or pigment dissolved or dispersed in the ink vehicle. If the colorant is a dye, the dye is typically present in a salt form. The ink vehicle comprises additional components depending on the application and desired properties of the color inkjet ink, as known in the art.
To produce high quality images, the inkjet ink must be compatible with the inkjet pen and the print medium. The properties of an optimal inkjet ink include, among others, good crusting resistance, good stability, low color-to-color bleed, and rapid dry time. In addition, the inkjet ink must be capable of passing through the inkjet orifice without clogging the orifice or puddling on the orifice plate. The inkjet ink should also permit rapid cleanup of the machine components with minimal effort. Although inkjet inks are known to possess one or more of the foregoing properties, few inkjet inks possess all of these properties because an improvement in one property often negatively impacts another property.
While the overall print quality of currently produced inkjet inks is generally high, puddling of these inks still occurs on the orifice plate of the printhead. Magenta inkjet inks typically exhibit worse puddling than cyan and yellow inkjet inks. Puddling occurs when the ink that is ejected through the orifices does not reach the print medium. Instead, the inkjet ink collects on an outer surface of the orifice plate or puddles adjacent to the edge of the orifice. This occurs when ink drops exiting the orifices leave behind minute amounts of ink on the orifice plate around each orifice. The extent of the puddling varies from a few, small drops of ink to the formation of large puddles on large portions of the orifice plate. Large puddles partially or completely block the orifices and cause missing nozzles, false low decap values, or changes in the trajectory of the ink drops. The change in trajectory results in the ink drop not hitting its targeted pixel center, which creates printing errors on the media and reduces the quality of the printed image.
Various solutions to address the problem of puddling have been proposed. Some solutions propose modifying the printhead or pen to reduce puddling, while other solutions modify the inkjet ink composition. For example, a coating of hydrophobic material is applied to the printhead to reduce its wettability and, thereby, reduce puddling. However, this modification to the printhead is costly. A combination of pen architecture and modifications to the inkjet ink composition have also been suggested to improve puddling.
Proposed modifications to the inkjet inks include adding anionic and nonionic surfactants to the inkjet ink. Similarly, adding a first surfactant and a second surfactant to improve puddling has been proposed. The first surfactant has a hydrophilic-lipophilic balance (“HLB”) value of 1.5 units lower than the second surfactant. Additional modifications include adding salts to the inkjet inks. However, adding salts or surfactants causes reliability and materials interaction issues because these additives cannot be used with all dyes or ink vehicles. In addition, adding surfactants or salts negatively affects desirable properties of the inkjet inks.
It would be desirable to improve puddling of inkjet inks by using additives that are effective in low amounts and do not negatively affect other properties of the inkjet inks. In addition, it would be desirable to use additives that are effective in many types of ink vehicles.